Expansion Tank Fix For Homeowners, Save Hundreds!

How to Check (and Replace) a Water Heater Expansion Tank

A Simple DIY Test That Can Prevent Costly Damage

At Wrench Warriors DIY, our goal is simple—save you money by showing you easy home fixes you can do yourself. Today’s tip is all about checking your water heater’s expansion tank to see if it’s good or bad.

This is a quick test you can perform with minimal tools, and catching a bad expansion tank early can prevent leaks, extend the life of your water heater, and save you from costly repairs.

Why Expansion Tanks Matter

Your water heater heats cold water, and as water heats, it expands. That extra volume has to go somewhere. An expansion tank absorbs the excess pressure through a rubber bladder inside the tank.

If the expansion tank fails, pressure builds in your water heater, and one of two things can happen:

• Your T&P (temperature & pressure) valve will start releasing water to relieve the pressure. - https://amzn.to/4lRTfNR

• You could experience serious water damage if the tank or lines burst.

In many cases, a failed expansion tank is linked to a bad pressure regulator, so if you’re having frequent issues, it’s worth checking both.

What You’ll Need

• A pair of pliers or a pipe wrench (pipe wrench if you need more grip strength)

• Pipe sealant or Teflon tape (or both)

• Bicycle pump and tire pressure gauge (for setting pre-charge on a new tank)

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Step 1: Shut Off and Drain Pressure

Before starting, turn off the water supply to your water heater. Then, relieve the system pressure by opening a hot water faucet or using the water heater’s drain valve.

Step 2: Remove the Expansion Tank

The expansion tank is mounted above or near the water heater, connected by piping. Carefully unscrew it, supporting its weight as you loosen it.

Pro Tip: Go slow—if the tank is full of water, it will be very heavy (like lifting a 5-gallon bucket). Be ready so it doesn’t drop on your foot or smash your fingers.

Step 3: Check the Weight

• If it’s light → The bladder inside is likely intact, and the tank is still good.

• If it’s heavy/full of water → The bladder has failed, and the tank needs to be replaced.

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Step 4: Choose the Right Replacement

Expansion tanks come in different sizes:

• Large tanks (bucket-sized) for homes with two water heaters. -

• https://amzn.to/3Jzb5aR

• Smaller tanks (soccer-ball-sized) for homes with one water heater. - https://amzn.to/4oW2DTd

Make sure your replacement tank is rated for potable water (safe for drinking water systems), not a boiler.

Step 5: Set the Pre-Charge Pressure (for New Tanks)

New expansion tanks typically come pre-charged at 45–50 PSI. If your home’s water pressure is higher (60–70 PSI), you’ll need to adjust it:

1. Remove the cap from the Schrader valve (air chuck) on top of the tank.

2. Use a bicycle pump to add air until it matches your home’s water pressure.

3. Check with a tire pressure gauge to confirm—65–70 PSI is a good target for most homes.

   
   

Step 6: Reinstall the Tank

1. Apply pipe sealant or Teflon tape to the threads. https://amzn.to/4lSExpM

2. Thread the tank into place by hand, then snug it with pliers or a wrench.

3. Avoid overtightening—you want a secure seal without damaging the threads.

If you use galvanized piping for your connection, it can support the weight of a failed tank until you replace it. This is a smart preventative setup.

Step 7: Turn On Water and Check for Leaks

Slowly turn your water supply back on. Wipe the connection area dry so you can quickly spot any drips.

And that’s it! You’ve just checked (and, if needed, replaced) your expansion tank. A five-minute inspection can save you hundreds in water damage and keep your system running smoothly.

If you need a replacement tank, check our link for the exact models we trust—they’re the same ones we install for our customers.